Due to users' increasing demand for perpetual and ubiquitous access to the Internet, the end-to-end wireless/wireline communications network is gradually migrating towards a flexible wireless and wireline IP infrastructure that supports heterogeneous multimedia (e.g., voice, video, data and the like) services in an economical manner. Thus, the Third Generation Partnership Project (3GPP) has been developing the specifications and architecture of an IP multimedia subsystem (IMS) that augments the existing circuit switched & 2G/3G wireless systems and expedites their gradual migration to an all IP infrastructure. IMS is built upon the open standard IP protocols defined by the IETF (Internet Engineering Task Force). It aims to serve as a ubiquitous IP service control and delivery platform for supporting all current services that existing circuit switched networks and the Internet offer as well as providing a vehicle for development and deployment of new services and applications in future.
The IMS technology defined by the 3GPP to provide IP Multimedia services over 3G mobile communication networks is set forth in 3GPP TS 23.228, Release 7 and TS 24.229 Release 8, which are hereby incorporated by reference in their entirety. IMS provides key features to enrich the end-user person-to-person communication experience through the integration and interaction of services. IMS allows new rich person-to-person (client-to-client) as well as person-to-content (client-to-server) communications over an IP-based network. The IMS makes use of the Session Initiation Protocol (SIP) to set up and control calls or sessions between user terminals (or user terminals and web servers). SIP is an example of an application level signaling protocol used by an initiating device to locate another device in order to establish a communication session. The Session Description Protocol (SDP), carried by SIP signaling messages, is used to describe and negotiate the media components of the session. Other protocols are used for media transmission and control, such as Real-time Transport Protocol and Real-time Transport Control Protocol (RTP/RTCP), Message Session Relay Protocol (MSRP), Hyper Text Transfer Protocol (HTTP).
FIG. 1(a) depicts the simplified layered architecture of a standard IMS, showing the transport, control, and applications layers of the network. The transport layer transfers bits and packets of information across the end-to-end platform, which comprises a set of heterogeneous networks including, but not limited, to the existing public switched telephone network-(PSTN), the Internet, a 2G/3G cellular network, a WLAN (wireless local area networks), and so on.
The IMS control layer is responsible for setting up sessions and allocating necessary resources for supporting users' services and applications. The IMS control layer primarily comprises the home subscriber server (HSS), call server control function (CSCF), and a set of edge controllers. The HSS, which stores and manages user subscription data, includes the IMS authentication, authorization, & accounting-(AAA) server as well as its master user profile database. Essentially, the HSS provides the functions of a master AAA and its profile database, very much equivalent to those of the home location registrar (HLR) and the Authentication Center (AuC) in GSM networks. The CSCF entity, which implements the session initiation protocol (SIP), is the session management and call control engine of the IMS. A CSCF also acts as a SIP registrar receiving registration information (e.g., public identity, private identity, contact, etc.), and stores them in the HSS that serves as a master AAA and user profile server. The IMS edge controllers are entities that facilitate the interworking of the IMS subnet with the existing wireless and wireline networks.
The IMS application layer includes a set of application servers (ASs) where an AS hosts and executes one or more IMS services/applications. The CSCF uses SIP to interact with ASs and vice-versa.
The 3GPP has adopted a highly centralized architecture in the development of the IMS specifications. It uses centralized application servers to support the various services/applications and a centralized platform to provide control layer functions (e.g., presence, AAA, and mobility management) necessary for running applications or offering services. In addition, centralized call controllers are used for session origination/modification/termination, quality of service control, and collecting charging data records. A key strength of IMS, its network-centric centralized architecture, is also the source of its main shortcomings. On the one hand, it allows the IMS to serve as a platform for efficiently supporting many services. On the other hand, it makes the introduction of IMS into legacy networks quite complex and costly. Moreover, the scalability, resiliency, and management flexibility of IMS are suboptimal.
To alleviate the shortcomings of the centralized IMS approach while supporting identical or at least similar services, US Patent Publication No. US 2008-0235778 A1 and US Patent Publication No. US 2008-0235185 A1 set forth a distributed architecture comprising an interconnected set of Edge Convergence Server (ECONS) customer premises equipments (CPEs). Hereafter, the said distributed architecture is referred to as ECONS architecture, the CPEs are referred to as ECONS CPEs, and the resulting IP multimedia communication network is referred to as ECONS system or ECONS network, interchangeably.
The tenet of ECONS architecture is to move most of the functions of the IMS application and control layers, as appropriate, into ECONS CPEs, which are distributed across the subscribers' homes and premises. Such a distributed architecture can reduce the cost of introducing IMS into legacy networks and improve the scalability, flexibility and resiliency of the overall system.
FIG. 1(b) depicts the simplified layered architecture of the ECONS approach in which many of the functions of the application layer and the control layer are moved to the ECONS CPEs at the user premises. The ECONS architecture is designed to provide an operator with a decentralized, low cost, scalable solution to deliver voice and multimedia services to its customers. Instead of relying on a costly and complex centralized core network, the ECONS architecture pushes the intelligence to the edge of the network by deploying ECONS CPEs on the subscriber's premises. The ECONS CPE provides session control functions and application servers, while the core network is limited to providing AAA services for the CPEs, and gateways to other networks. The functional ECONS CPE may be embodied in a residential gateway, set top box, media center or the like.
The following description sets forth some of the main characteristics of the ECONS architecture. First, the ECONS is a distributed networking system. Instead of relying on a centralized core network, the main functionality of the ECONS system is provided by the ECONS CPE. The ECONS CPEs provide user registration and session management, authentication, media gateway, application servers and call control functions for user equipments (UEs) such as cell phones and the like. The core network provides authentication for CPEs and interworking functions with other networks. Second, the ECONS architecture is scalable. As the number of subscribers increases, so does the number of deployed CPEs, thus growing as required. Third, the ECONS architecture can operate in a peer to peer as well as client server manner. Whenever possible, the communication happens at the edge of the network with minimal intervention by the network core. Signaling and media are transferred directly between CPEs, without being relayed by the core network. Fourth, the ECONS architecture provides advanced functions to its users with minimal involvement of its core network. In particular, several UEs can be associated with the same CPE. Fifth, as in IMS, the session management and control in ECONS system is performed using the SIP protocol. An ECONS system can interoperate with other SIP networks, including IMS.
In summary, an ECONS system is a distributed IP-centric control and signaling platform comprising a set of CPEs residing at the subscribers' premises which provides voice, video, data, and multimedia services to fixed and mobile subscribers. Each ECONS CPE comprises presence, location, session management, resource management, AAA, NAT traversal, CPE management enablers as well as the standard TCP/IP stack, and possibly a DSL/Cable modem for access to the Internet. The CPE is controlled and possibly owned by the operator rather than the subscriber.
FIG. 2 depicts the functional architecture of an ECONS network 200. It should be emphasized that in this implementation the circuit switched network 220 and the broadband IP network 230 both belong to and are operated by the same operator. The ECONS network comprises a set of ECONS CPEs 210 connected to the operator's core network. The ECONS core network comprises the operator's circuit switched and broadband IP networks 220 and 230. An individual ECONS CPE 210 may be connected to the operator's broadband IP network 230 or to both its broadband IP network 230 and its circuit switched network 220. Although the ECONS architecture envisions moving most of the control and application layers functions of IMS into ECONS CPEs, it still maintains in the core network a set of common functions that operators deem essential to proper operation and security of the network (e.g., AAA server, NAT traversal, etc.).
More specifically, the functional entities in the ECONS network are the ECONS CPE 210 and the operator's control platform 240 in its core network. The operator's control platform of the ECONS core network includes a RENDEZVOUS server 242, a NAT traversal server 270, a DNS server 246, a SIP proxy 248, a VoIP gateway 250 and an authentication, authorization, and an accounting (AAA) server 252.
The ECONS CPE 210 is the central entity of the system 200. It comprises a SIP-based session manager, a policy repository, and application servers such as a presence server, web server, etc. The session manager of the ECONS CPE may control every communication flow initiated or received by the UE 260. It may add or drop call/session legs, route sessions to any endpoint, and seamlessly move a session to any end points. The ECONS CPE 210 provides control over all audio and video sessions of the UEs 260. It is responsible for routing SIP signaling to other ECONS CPEs as well as to other SIP devices. It also provides a local proxy/registrar for SIP based UEs, and the gateway functionality for POTS (plain old telephone service) equipments. It may also include some application servers, such as a presence server. It is important to note that the ECONS CPE 210 is installed in the user's home network. It may include a broadband modem, in which case it is connected directly to the broadband network. It can also be connected through an Ethernet link to an external broadband modem, which may implement a network address translator (NAT) 270. In this case the ECONS CPE 210 provides the necessary mechanisms for NAT traversal for SIP signaling and media.
The rendezvous server 242 of the ECONS core network provides a simple way for a CPE to reach any other CPE in the system. Every ECONS CPE 210 maintains an active connection with the RENDEZVOUS server 242. This connection can be used to send a short message to any other ECONS CPE. It is mainly used for NAT traversal. When two ECONS CPEs 210 want to establish a SIP session, they determine their public IP addresses using STUN (Simple Traversal of UDP thru NATs) protocol, and then they send their public addresses to each other through the RENDEZVOUS server 242. After these addresses have been exchanged the rest of the communication is done directly between the CPEs without the intervention of any other node.
The STUN server 244 is the NAT Traversal that supports the STUN protocol and the relay usage of that protocol The STUN protocol is used by a node behind a NAT (which in the case of ECONS is an ECONS CPE) to find its own public address, determine the NAT type and the Internet side port associated by the NAT with a particular local port. The STUN server 244 also supports the relay usage. In the relay usage the server allocates a public IP address and port that the client can use for communications through the NAT. Note that in the relay usage data has to be relayed through the core of the network, which is, of course, less efficient. The detailed specifications of STUN are presented in RFC 3489.
The DNS server 246 of the provider's control platform 240 includes entries identifying the SIP servers for the provider's domain, an ENUM database, and the list of available STUN servers. Note that “ENUM” is a protocol that resolves fully qualified telephone numbers to fully qualified domain name addresses using a DNS-based architecture. The DNS specifications are set forth in RFC 1034 and RFC 1035.
The SIP proxy 248 is used to route SIP signaling between external networks and the ECONS CPEs. The SIP proxy 248 can receive SIP requests from non-ECONS SIP devices and route them to the appropriate ECONS CPE. The SIP specifications are set forth in RFC 3261.
The VoIP gateway 250 provides signaling and media gateway functionalities to interwork the circuit switched network with the ECONS network.
The AAA server 252 provides AAA services for the ECONS CPEs. It comprises an ECONS profile server as well as AAA engine that authenticates the CPEs. It also stores the billing records resulting from calls to the circuit switched domain. In principle, the AAA server 252 functionality is equivalent to those of a HSS in a centralized IMS.
Cellular operators deploy low power base stations at subscribers' premises to improve their indoor cellular coverage. These base stations are often referred to as femto cells in the cellular industry generally and as Home NodeBs in the 3GPP community in particular. These femto cells are attached to the cellular operator's core network and its centralized IMS services. Three options are currently considered for femto cell connectivity to the core network: Iu-b over IP, RAN Gateway, and SIP/IMS. First, the Iu-b over IP option uses the existing 3GPP Iu-b interface to leverage the cellular operators' 3G Radio Node Controllers (RNCs) to support these femto cells, through a remote gateway along with the 3G NodeBs (i.e., 3G BTSs). Note that the Iu-b interface is primarily proposed for connection of 3G NodeBs with 3G RNCs. Second, the RAN Gateway approach uses a network controller residing between the cellular operator's core network and its IP access network to connect the femto cells to the cellular core network. Third, the SIP/IMS solution proposes to use SIP between femto cells and the IMS core of the cellular operator.
As the number of femto cells increases the cellular operator will eventually have in place two parallel wireless infrastructures that overlap in coverage: a series of conventional cells that each, for example, cover a distance of about 3 to 5 kms and a series of femto cells that each, for example, cover a distance of about 30-100 m. The conventional cells will be referred to herein as macrocells to distinguish them from the femto cells. Of course, the coverage offered by the femto cell infrastructure will be more complete and more fully overlap with the macrocellular infrastructure in dense metropolitan areas than in less densely populated areas. In such densely populated areas, or in an enterprise environment such as a corporate or university facility or campus, the cellular operator may be able to use the femto cell infrastructure as an alternative wireless platform to the macrocellular infrastructure.
One problem with using the femto cell infrastructure in this manner is ensuring seamless mobility (i.e., seamless hand-off of the UE) of the user across the femto cell infrastructure. To ensure such a seamless mobility or hand-off the UE will need to be authenticated (or re-authenticated) each time it moves from one femto cell to another. In addition, the packets destined for the UE should be forwarded to the UE as it changes its point of attachment to the network from one femto cell to another femto cell.
These processes, particularly the authentication (re-authentication) of the UE, are problematic because the amount of time it may take a user equipped with a UE to move (e.g., by walking) from femto cell to femto cell may be about the same or less than the amount of time needed by conventional hand-off techniques to transition a UE from one femto cell to another. Clearly, conventional hand-off techniques generally will not be suitable for use with a femto cell infrastructure.